For me, there is a fairly clear argument that works - online banking, you will know if there is a problem (the money is gone), online voting, you might not even

For me, there is a fairly clear argument that works - online banking, you will know if there is a problem (the money is gone), online voting, you might not even _know_ it was compromised (in a close election, skewing a few percent of the votes could change the results without it being significantly different to the polls).